Color image processing apparatus

ABSTRACT

There is provided a color image processing apparatus comprising color conversion circuit for converting image data to a desired color, feature extraction circuit for extracting a feature of the image data and image correction circuit for correcting the image data on the basis of the feature extraction circuit, characterized in that a color conversion processing is executed prior to extraction of feature from the image data.

This application is a continuation of application Ser. No. 07/436,256filed Nov. 14, 1989, now U.S. Pat. No. 4,982,277.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color image processing apparatus.

2. Related Background Art

Hitherto, as is also known as a color laser copier or the like, forinstance, a color image processing apparatus having a complicatedediting function, a color converting function, and the like using adigital image processing technique has been invented.

A color image processing apparatus as shown in FIG. 3 has been proposedas an apparatus having such character processing function, colorconverting function, and editing function.

In such an apparatus, in accordance with the level of Bk which iscalculated by primary signals Y, M, and C which were color separated,the Y, M, and C signals are subtracted and the Bk signal is increasedand the edge is emphasized in accordance with the level which iscalculated from Min (Y, M, C). Due to this, the edge portion of a blackcharacter is replaced to a single black portion as much as possible,thereby improving the quality of character. However, in such an imageprocessing system, if a color conversion circuit is arranged after thecolor correction circuit, in the case of executing a color convertingprocess to convert a chromatic character into a black character by thecolor conversion, the chromatic character cannot obviously be extractedas a black character in a black extraction section. Therefore,subtraction amounts of Y, M, and C are small, so that the color isdetected in the color conversion section and is color converted so as toobtain black. On the other hand, since the value of Min (Y, M, C) issmall in the black extraction section, a level determination sectionreduces the edge emphasis in an edge emphasis section as compared withthe case of black.

Therefore, the ordinary black character becomes a sharp image by theedge emphasis. However, there occurs an inconvenience such that thecharacter which was converted into black by the color conversion becomesa dull character.

Although the above example has been described with respect to the imageprocess which is executed to a black character, even if the kind of suchan image process is another kind of process, if the apparatus isconstructed as in the conventional one, an inconvenience correspondingto the process occurs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image processingapparatus which can solve the above problems.

Another object of the invention is to provide an image processingapparatus which can execute both of a process to extract characteristicsor the like and a color converting process.

Still another object of the invention is to provide an image processingapparatus which can accurately extract characteristics even whenexecuting a process such as a color conversion or the like.

Under such objects, according to a preferred embodiment of theinvention, there is disclosed an image processing apparatus comprisingcolor converting means for converting image data into a desired color,characteristic extracting means for extracting the characteristics ofthe image data, and image correcting means for correcting the image datain accordance with the characteristics extracted by the characteristicextracting means, wherein the color converting process is executedbefore the characteristics of the image data are extracted.

Further another object of the invention is to provide an imageprocessing apparatus which can easily execute the processes for colorconversion, character correction, and the like to a color image signalobtained by being read.

The above and other objects and features of the present invention willbecome apparent from the following detailed description and the appendedclaims with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a construction of an embodiment 1 ofthe present invention;

FIG. 2 is a circuit diagram of a color conversion 2;

FIG. 3 is a diagram showing a conventional example;

FIG. 4 is a block diagram of an embodiment 2;

FIG. 5 is a block diagram of an embodiment 3;

FIGS. 6, 6A and 6B are block diagrams for a black character process;

FIG. 7 is a diagram of a calculating circuit of a YIQ signal;

FIG. 8 is a diagram of a calculating circuit of an achromatic signal W;

FIG. 9 is a diagram of a black generating circuit;

FIG. 10 is a diagram of a black level determination circuit;

FIG. 11 is a diagram of an edge signal calculating circuit;

FIG. 12 is a diagram of an image area determination circuit; and

FIG. 13 is a diagram of a black character correction circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to an embodiment of the invention which will be explainedhereinlater, there is shown an apparatus in which by using aconstruction such that the color converting process is executed beforethe color correcting process, the picture quality of the color convertedimage and the picture quality of the image which is not color convertedare equalized, and the deterioration in picture quality due to acontradiction when respective functions are combined is eliminated.

The invention will be described hereinbelow with reference to thedrawings.

Embodiment 1

FIG. 1 shows an embodiment of the invention. Color image signals whichare obtained by converting image signals from color sensors (forinstance, R, G, B) (not shown) into digital signals by A/D convertersare converted such that white=OOH and black=FFH in accordance with therelative luminous efficiency characteristics of the human eyes bylogarithm converting circuits. Thus, the Y, M, and C signalscorresponding to the concentration value are obtained.

The digital signals of Y, M, and C obtained from an image readingsection (not shown) are input to a color conversion section 1.

As shown in FIG. 2, in the color conversion section 1, a check is madeby three window comparators 7, 8, and 9 to see if the image data of Y,M, and C denote the colors which are color converted or not. If they arethe colors to be color converted, a selecting signal 13 is set to thehigh "H" level and preset image data Y',M', and C' after completion ofthe color conversion are selected by a CPU (not shown) and the colorconverting processes are executed.

In FIG. 2, Y_(max), Y_(min), M_(max), M_(min), C_(max), and C_(min)denote registers to store data which are set from the CPU through a CPUBUS for controlling the apparatus of the embodiment.

Y', M', and C' indicate registers to store the color data ofpredetermined colors after completion of the conversion. Outputs of theregisters are input to B input terminals of selectors 10, 11, and 12,respectively.

The color data of the input image are input to A input terminals of theselectors 10, 11, and 12, respectively. Outputs of the windowcomparators 7, 8, and 9 are supplied to an AND gate and the AND of themis calculated. An output of the AND gate is input to the selectors 10 to12.

In the above construction, if the window comparators 7 to 9 determinethat the color data of the input image lies within a predetermined rangewhich has been set in each of the registers Y_(max), Y_(min), M_(max),M_(min), C_(max), and C_(min), the selectors 10 to 12 are switched so asto output the data which is input to each B input terminal, therebyexecuting the color converting operation.

The outputs of the color conversion section 1 are input to a colorcorrection section 2 and a black extraction section 5. The colorcorrection section 2, black extraction section 5, a level determinationsection 6, and an edge emphasis section 4 are well known.

Embodiment 2

FIG. 4 shows the embodiment 2 of the invention. Image signals from colorsensors (for instance, R, G, B) 0 are converted into digital signals byA/D converters. The resultant color digital image signals R, G, and Bare converted into the R, G, and B signals of the NTSC by an NTSCconversion section 17. The NTSC conversion section comprises well-known3×3 primary processing circuits.

The image signals which were converted into the R, G, and B signals ofthe NTSC are input to the color conversion section 1. The colorconversion section 1 is similar to that shown in FIG. 1. The colorconversion in the image signals of the R, G, and B systems can be alsoexecuted in a manner similar to the embodiment 1 by settingcorresponding parameters of the image signals such that Y→B, M→G, C→R,Y'→B', M'→G', C'→R', Y_(max) →B_(max), Y_(min) →B_(min), M_(max)→G_(max), M_(min) →G_(min), C_(max) →R_(max), and C_(min) →R_(min).

After the color conversion of the RGB system was executed as mentionedabove, the resultant R, G, and B data are input to a logarithmconversion section 16, so that the image signals of the YMC systemaccording to the relative luminous efficiency characteristics of thehuman eyes as mentioned above are obtained.

Since the color correction section 2, black extraction section 5, leveldetermination section 6, and edge emphasis section 4 are incorporated inthe well-known technique as mentioned above, their descriptions areomitted.

Embodiment 3

FIG. 5 shows an embodiment 3 of the invention. The NTSC conversionsection 17, color conversion section 1, and logarithm conversion section16 are similar to those in the embodiment 2.

The color correction section 2 is the well-known technique and is acircuit to correct the concentration signals of C, M, and Y into the C,M, Y, and K signals according to an output apparatus.

FIGS. 6A and 6B show an example of a circuit construction of a blackcharacter processing section 18. In FIGS. 6A and 6B, reference numeral10 denotes a YIQ signal calculating circuit to calculate a luminancesignal Y and color signals I and Q from the R, G, and B signals of thecolor conversion section 1. The luminance signal Y is inverted into adarkness signal Y by an inverter 30 to obtain an edge signal of a blackcharacter. Thereafter, the edge signal is extracted by executing theLaplacian operation by a black edge generating circuit 40 and a KEsignal is output. The I and Q signals are signals indicative of thecolor differences from an achromatic color and are input to anachromatic color signal calculating circuit 20. An achromatic colorsignal W is output from the calculating circuit 20 by using a look-uptable. The W signal indicates that the color approaches the achromaticcolor as the value of the W signal is large. The W signal and Y signalare input to a black level determining circuit 50. The circuit 50combines the W and Y signals and outputs a T signal. Practicallyspeaking, the signal indicative of a degree of black is output as a Tsignal by a binary or more value. The black edge generating circuit 40outputs black character edge signals E₁ and E₂ from the black edgesignal KE in accordance with the black level signal. The E₁ signal is asignal to emphasis the edge of the black character. The E₂ signal is asignal to eliminate a color deviation of the edge of the blackcharacter. An image area signal generating circuit 70 determines that anarea of the bright chromatic color and areas near it are an image areaon the basis of the W signal and Y signal and outputs an image areadetermining, signal Z. A black character correcting circuit 80 correctsC (cyan), M (magenta), Ye (yellow), and K (black) by using the blackcharacter edge signals E₁ and E₂ from which an erroneous discriminationwas eliminated by the image area signal Z. That is, the E₂ signal isadded as a correction signal to the C, M, and Y signals and the E₁signal is added as a correction signal to the K signal. The resultantcorrected signals are input to an output apparatus such as color printerlike, for instance, a color LBP 95 or the like, color monitor, or thelike at the next stage.

A block of each circuit shown in FIGS. 6A and 68 will now be described.

(1) In FIGS. 6A and 6B mentioned above, reference numeral 10 denotes YIQsignal calculating means which receives the RGB signals as inputsignals. The YIQ signal calculating circuit 10 will now be describedwith reference to FIG. 7. In FIG. 7, reference numerals 25, 26, and 27denote multipliers to multiply the RGB signals with predeterminedparameters a_(ij) (i, j=1, 2, 3). Reference numeral 28 denotes a memoryin which the parameters a_(ij) are stored; 29 indicates a selector toselect the proper parameters which are multiplied to the R, G, and Bsignals; 37 an adder to add outputs of the multipliers 25, 26, and 27;and 38 a selector to select an output of the adder 37 to each of the Y,I, and Q signals. The Y, I, and Q signals are expressed by using the R,G, and B signals and the parameters a_(ij) as follows.

    Y=a.sub.11 ×R+a.sub.12 ×G+a.sub.13 ×B,

    I=a.sub.21 ×R+a.sub.22 ×G+a.sub.23 ×B,

    Q=a.sub.31 ×R+a.sub.32 ×G+a.sub.33 ×B

(2) In FIGS. 6A and 6B, reference numeral 20 indicates the achromaticcolor signal calculating circuit. FIG. 8 shows an internal constructionof the achromatic color signal W calculating circuit. Reference numeral21 denotes a multiplier to output the square of the I signal; 22indicates a multiplier to obtain the square of the Q signal; 23 theadder for adding outputs of the multipliers 21 and 22 and outputting I²+Q² ; and 24 a look-up table to determine the output W in accordancewith the result of I² +Q². The output W of the look-up table 24 isdetermined by the following equation. ##EQU1##

(3) In FIGS. 6A and 6B, as mentioned above, the inverter 30 inverts theY signal and outputs the Y signal.

(4) In FIGS. 6A and 6B, reference numeral 40 indicates the black edgeamount KE generating circuit. An internal construction of the black edgegenerating circuit will now be described with reference to FIG. 9.Reference numerals 31, 32, 33, 34, and 35 denote line buffers in whichan objective pixel is set to the center. Reference numeral 36 denotes acomputing circuit to calculate the edge amount. Assuming that valuesx_(ij) (i, j=1, 2, 3, 4, 5) have been stored in the line buffers, theobjective pixel is expressed by x₃₃ =Y. The edge amount KE is obtainedby the following equation.

    KE=x.sub.33 -(x.sub.11 +x.sub.15 +x.sub.51 +x.sub.55)/4

(5) In FIGS. 6A and 6B reference numeral 50 denotes the black leveldetermining circuit. FIG. 10 shows an internal construction of the blacklevel determining circuit. Reference numeral 51 indicates a multiplierto multiply the signals Y and W. Reference numeral 52 represents athreshold processing circuit for processing an output u of themultiplier 51 and outputting the resultant data as a black level signalT in a manner such that: 0 if u<T₀ ; 1 if T₀ ≦u<T₁ ; 2 if T₁ <u<T₂ ; and3 if T₂ ≦u.

(6) In FIGS. 6A and 6B, reference numeral 60 represents a blackcharacter edge generating circuit for outputting two kinds of edgesignals E₁ and E₂ on the basis of the black edge signal KE and blacklevel signal T.

FIG. 11 shows a construction of the edge generating circuit 60.Reference numeral 61 denotes a comparator to compare the value of the KEsignal with a threshold value stored in a memory 62. When the KE islarger than the threshold value, 1 is output. When the KE is equal to orsmaller than the threshold value, 0 is output. Reference numeral 62denotes the memory to store a predetermined threshold value, and 63indicates a processing circuit for obtaining the edge signal E₁ from theKE signal, the T signal, and an output of the comparator 61.

Practically speaking, the processing circuit 63 outputs E₁ =0 when theoutput of the comparator 61 is 0 and outputs E₁ =α₁ ×KE when the outputof the comparator 61 is 1. α₁ denotes a constant which is properlydecided in dependence on the value of T and E₁ is expressed. Referencenumeral 64 indicates a comparator for comparing the value of KE with athreshold value stored in a memory 65. When the KE is larger than thethreshold value, 1 is output. When the KE is equal to or smaller thanthe threshold value, 0 is output. Reference numeral 65 denotes thememory in which a predetermined threshold value is stored. Referencenumeral 66 represents a processing circuit to obtain the edge signal E₂from the KE signal, the T signal, and an output of the comparator 64."0" is stored as a threshold value in the memory 65. When the output ofthe comparator 64 is 0, the processing circuit 66 outputs E₂=KE×(-1)×α₂. When the output of the comparator 64 is 1, E₂ =KE×α₂ isoutput. α₂ is a constant which is properly determined by the value of Tand E₂ is expressed.

(7) In FIGS. 6A and 6B, reference numeral 70 denotes the image areasignal generating circuit. FIG. 12 shows an internal construction of theimage area signal generating circuit 70. In FIG. 12, reference numeral71 denotes a multiplier for multiplying the Y signal and the W signalobtained by inverting the W signal, thereby obtaining an X signal.Reference numeral 72 denotes a threshold processing circuit forcomparing the X signal with a predetermined threshold value andoutputting the result of the comparison between them. Reference numerals73, 74, and 75 indicate line buffers to store an output of the thresholdprocessing circuit 72. Reference numeral 76 represents a determiningsignal processing circuit for reading out values of the line buffers 73,74, and 75 around the objective pixel and discriminating whether theobjective pixel lies within the image area or not. If it lies within theimage area, 1 is output as an image area signal Z. If the objectivepixel is out of the image area, 0 is output as the image area signal Z.

(8) In FIGS. 6A and 6B, reference numeral 80 denotes the black charactercorrecting circuit. FIG. 13 shows an internal construction of the blackcharacter correcting circuit 80. Reference numeral 82 denotes a gate foroutputting 1 when the black level is not 0 and the image areadetermining signal Z is 0 and outputting 0 in the other cases on thebasis of the black level signal T and the image area determining signalZ. Reference numeral 83 indicates a selector to output E₁ '=E₁ and E₂'=E₂ when an output of the gate 82 is 1. The selector 83 outputs E₁ '=0and E₂ '=0 when the output of the gate 82 is 0. Reference numeral 84denotes an adder to add the E₂ ' signal to the C signal; 85 indicates anadder to add the E₂ ' signal the M signal; 86 an adder to add the E₂ 'signal to the Y signal; and 87 an adder to add the E₁ ' signal to the Ksignal.

In the above apparatus, the edge emphasis is executed with respect tothe area which was determined to be a character portion, while the edgeemphasis is not executed with respect to the area which was decided tobe a dot color image.

Since the black character process has been executed after the colorconverting process of the color conversion circuit 1 as shown in FIGS. 1and 5, as compared with the case where the color converting process isperformed before the black character process, an erroneousdiscrimination in the black character process can be prevented and theaccurate process can be executed.

In the embodiments of the invention described above, an edge of theblack or achromatic color portion has been extracted for the blackcharacter process as an extraction of the characteristics of an image.However, the invention is not limited to such an edge extraction. Theinvention can be also similarly applied to other characteristicextracting process or the like to extract other characteristics suchthat, for instance, only the portion of a special color component isextracted and the other portions are masked.

As described above, according to the embodiments, by executing the colorconverting process before the characteristic extracting process, theerroneous discrimination in the characteristic extraction can beprevented and a good picture quality is obtained.

What is claimed is:
 1. A color image processing apparatuscomprising:inputting means for inputting a color image signal;conversion means for converting said color image signal inputted by saidinputting means to a color image signal defined by standard color space;color conversion means for performing predetermined color conversion onsaid color image signal defined by standard color space converted bysaid conversion means; and color correction means for performing a colorcorrection to output the color image signal defined by standard colorspace converted by said color conversion means to an output device.
 2. Acolor image processing apparatus according to claim 1, wherein saidcolor image signal defined by standard color space is an NTSC standardsignal.
 3. A color image processing apparatus according to claim 1,wherein said inputting means comprises a color sensor.
 4. A color imageprocessing apparatus according to claim 1, wherein said color conversionmeans comprises:extracting means for extracting a signal correspondingto a predetermined color from said color image signal defined bystandard color space; and replacing means for replacing said signalcorresponding to said predetermined color extracted by extracting meanswith a signal corresponding to another color that is different from saidpredetermined color.
 5. A color image processing apparatus according toclaim 1, wherein said color correction means corrects said color imagesignal defined by standard color space to a four color signal of yellow,magenta, cyan and black.
 6. A color image processing apparatus accordingto claim 5, further comprising means for outputting a signal correctedby said color correction means to a color printer.
 7. A color imageprocessing method comprising the steps of:inputting a color imagesignal; converting the color image signal inputted in the inputting stepto a color image signal defined by standard color space; performingpredetermined color conversion on the color image signal defined bystandard color space converted in the conversion step; and performing acolor correction to output the color image signal defined by standardcolor space converted in the color conversion step to a output device.8. A color image processing method according to claim 7, wherein thecolor image signal defined by standard color space is an NTSC standardsignal.
 9. A color image processing method according to claim 7, whereinthe inputting step is performed by a color sensor.
 10. A color imageprocessing method according to claim 7, wherein the color conversionstep comprises the steps of:extracting a signal corresponding to apredetermined color form the color image signal defined by standardcolor space; and replacing the signal corresponding to the predeterminedcolor extracted in the extracting step with a signal corresponding toanother color that is different from the predetermined color.
 11. Acolor image processing method according to claim 7, wherein the colorcorrection step corrects the color image signal defined by standardcolor space to a four color signal of yellow, magenta, cyan and black.12. A color image processing method according to claim 11, furthercomprising the step of outputting a signal corrected in the colorcorrection step to a color printer.